Ignition circuits using gate controlled switches



Feb. 28, 1967 J. w. MOTTO, JR. ETAL 3,306,274

IGNITION CIRCUITS USING GATE CONTROLLED SWITCHES Filed July 23. 1964 FIG. I.

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LI Y r R2 80 RUN OFF INVENTORS BY RUN OFF United States Patent Ofilice 3,306,274 Patented Feb. 28, 1967 3,306,274 IGNITIUN CIRQUITS USING GATE CGNTROLLED SWITCHES John W. Motto, Ira, Greensburg, and Warren S. Fry, Connellsville, Pa, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed July 23, 1964. Ser. No. 384,675 4 Claims. (Cl. 123148) The present invention relates to ignition systems, and more particularly to ignition systems employing a single semiconductor switching device.

Practically all automobiles of today employ a mechanical breaker type of ignition system. The mechanical breaker type of system introduces several limitations in the functioning of an internal combustion engine. The most severe limitations are: low life expectancy of the mechanical breaker points; lost spark energy due to the poor switching of breaking points, especially during startup and as the points degradate; and attenuation of spark voltage at high engine speeds. The probable life expectancy of presently used mechanical breaker points is at most 10,000 miles. The limited life expectancy is principally due to mechanical switching operation and the arcing produced between the ignition points during the switching operation. .The operating levels of ignition points presently used in automobile engines are approximately 300 to 400 volts at 3 to 6 amperes. At such voltages and currents the points are quickly degraded by the severity of arcing produced. Furthermore, with even a partial degradation of the ignition points, for example, after only 5,000 miles of usage, a substantial impairment in the efiiciency of operation of the engine will become evident. The reasons for this are that the spark energy is lost 'by poor switching of the breaker points after the breaks have been somewhat degraded and also due to the lack of uniformity in switching over the many switching cycles. The mechanical switching problem is especially severe during the cranking or starting up operation of the engine, where the breaker points are being switched at relatively low speeds and a large amount of spark energy is required to start the engine.

As efficiency and horsepower requirements for modern automobile engines increase, higher engine speeds and higher compression ratios are required. At higher engine speeds on higher compression ratios, great demands are placed on the ignition system to supply a. large enough spark voltage within a limited time period. In the usual case, a set of ignition points are opened for one half of the switching cycle, while energy is being supplied to the ignition coil; and the ignition points are close-d for the second half of the cycle, while the spark energy is being supplied to the distribution circuit. Therefore, as engine speed increases, there is less time for energy to be supplied to the ignition coil and then be dissipated in the distributor and spark plug arrangement. It can readily be seen as the speed of the engine increases, the quality and magnitude of the spark output voltage will decrease and detract from the efficiency of operation of the engine in that it will be more difficult to adequately fire the spark plugs with only the limited amount of spark voltage applied thereto over a brief span of time.

These disadvantages and limitations of mechanical breaker point ignition systems may be overcome through the use of ignition circuits using a semiconductor switching device, termed therein as a gate controlled switch (GCS). The gate controlled switch or as it sometimes is called a semiconductor thyratron or a semiconductor switch having a gate turn-01f characteristic, is a four layer, three terminal, solid state switching device having characteristics similar to those of the conventional silicon controlled rectifier (SCR). The GCS possesses the desirable characteristics of the SCR such as: high blocking voltages, high surge ratings and pulse turn-on. But, over and above this, the GCS has a unique ability of being turned olf by the application of a negative pulse voltage to its gate electrode, without the necessity of reducing the anode current to below the holding value. This unusual gate turn-off characteristic provides very desirable results when utilized in ignition circuits as will be fully discussed herein.

It is therefore an object of the present invention to provide a new and improved ignition circuit utilizing a gate controlled switch in which may readily be incorporated into existing ignition systems.

It is a further object of the present invention to provide a new and improved ignition circuit utilizing a single gate controlled switch and wherein the circuit utilizes a minimum number of components.

It is a further object of the present invention to provide a new and improved ignition system utilizing a gate controlled switch which provides long life for breaker points, low loss in spark energy and small attenuation of spark voltage at high engine speeds.

Broadly, the ignition system of the present invention provides a gate controlled switch which is render-ed nonconductive in response to the position of a set of ignition points; thus inducing a voltage in an ignition coil to be transferred as a spark output voltage. The gate controlled switch is then rendered conductive after a predetermined time to permit the buildup of energy in the ignition coil.

These and other objects and advantages will become more apparent when considered in view of the following specification and drawings in which:

FIGURE 1 is a schematic diagram of one embodiment of the present invention.

FIG. 2 is another embodiment of the present invention wherein the ignition points are isolated from ground:

FIG. 3 is a schematic diagram of another embodiment of the present invention; and

FIG. 4 is a schematic diagram of still another embodiment of the present invention.

. Referring to FIG. 1, it is assumed initially, as shown, that an oifrun switch S0, is in its closed run position and, a set of ignition points Si, is in its closed position. The set of ignition points Si is shown schematically and may, for example, be the common mechanical breaker type which open and close in timed sequence in response to the rotation of the cam shaft of an internal combustion engine. With the switches S0 and Si in the state shown, a gate controlled switch G will be in its conductive, turned on state. The gate'controlled switch G includes an anode electrode a, a cathode electrode k and a gate electrode g. An ignition transformer IT has its primary ignition winding W1 connected in series to the anode electrode a. While the gate controlled switch G is conductive from its anode to cathode electrodes, a current path is provided from a battery E, which has its positive electrode connected to ground, through the primary ignition coil W1. A current limiting resistor R2 is connected between the cathode electrode k and one terminal of the run-off switch S0. The negative electrode of the battery E is connected to the other end of the switch S0 to complete the circuit. The ignition transformer IT may be of the type commonly found in automobiles. The ignition transformer IT has a secondary ignition coil W2 inductively coupled to the primary ignition coil W1. An output terminal To is connected to the ungrounded end of the secondary coil W2 and from which an output spark voltage is obtained and may be provided to a distributor circuit, not

shown, for its subsequent distribution to the various spark plugs of an internal combustion engine. The battery E may for example be a 12 volt multicell type commonly used in automobiles.

One side of the set of ignition points Si shown in FIG. 1 is grounded, the other end is connected in series with a resistor R1 and an inductor L1, a junction J1 being formed between the resistor R1 and the inductor L1. The opposite end of the inductor L1 is connected to the cathode electrode k of the gate controlled switch G. The gate electrode g of the gate controlled switch G is directly connected to the junction J 1. With the switch set of ignition points Si closed, as initially assumed, a current path will also be provided from the battery E through the switch Si, the resistor R1, the inductor L1, the resistor R2, the switch S to the battery E. A positive potential will thus be applied to the gate electrode connected to the junction J1 to maintain the gate controlled switch G in its conductive, turned on state. To render the gate controlled switch non-conductive, the set of ignition points Si is opened. Since th inductor L1 will not permit current passing therethrough to change instantaneously, a negative voltage will be induced across the inductor L1 which will be applied to the gate electrode g. This negative pulse voltage will cause the gate controlled switch G to be rendered non-conductive, that is, turned off, with an opened circuit provided between its anode and cathode electrodes.

Due to the sudden change of current in the anode-cathode circuit of the gate controlled switch G, a relatively high voltage will be induced in the primary ignition coil W1 connected in series therewith. This voltage then will be transformed to the secondary ignition coil W2 to provide a high output spark voltage at the terminal To connected at the secondary ignition coil W2.

To complete the cycle the set of ignition points Si is again closed to provide a conductive path through the resistor R1 and the inductor L1 so that a positive potential is applied to the gate electrode g. The gate controlled switch G will thus be rendered conductive to provide a conductive path from the battery B through the ignition winding W1 so that energy for the next output of spark voltage may be stored by the building up of current in the primary ignition winding WI.

The circuit shown in FIG. 1 provides a very simple ignition system requiring only a limited number of additional components. That is, the only added components required are the gate controlled switch G, the inductor L1 and the resistor R1 in order to provide a workable system with components already utilized in standard ignition systems.

FIG. 2 is an adaptation of the ignition circuit of FIG. 1 for use with a negative ground ignition system, the circuit of FIG. 1 being a positive ground system. In th circuit of FIG. 2, the ignition points Si are isolated from ground wherein in FIG. 1 one side of the switch Si is connected at ground. The isolation of the ignition points Si from ground is necessary when a negative ground system is to be used in the automobile. The circuits of FIGS. 1 and 2 are substantially the same except that in FIG. 2 the negative electrode of the battery E is grounded with the current limiting resistor R2 and the off-run So being placed on the positive side of the battery E. Similarly, as in FIG. 1, the gate controlled switch G has connected in series with its anode-cathode circuit the primary ignition coil W1. The secondary ignition coil W2 has one end connected to the anode electrode a, so to provide the proper polarity output signal at the terminal To. Across the primary ignition coil W1 and the gate controlled switch G to ground is connected a series circuit including a set of ignition points Si, a resistor R1 and an inductor L1. The gate electrode g is connected to the junction J1 between the resistor R1 and the inductor L1.

The circuit of FIG. 2 operates identically with that of FIG. 1, that is, with the switches S0 and Si closed, the gate controlled switch G will be conductive with the current flowing in the ignition coil W1 and through the inductor L1. When the ignition points Si are opened,

a negative voltage will be induced across the inductor L1, which will apply a pulse to the gate electrode to thereby turn off the gate controlled switch G. The sudden turning off of the gate controlled switch G will induce a relatively high voltage in the primary ignition coil W1 which will be transferred to the secondary ignition coll W2 by transformer action. An output spark voltage will then be provided from the output terminal To. Upon closing the set of ignition points Si again, the gate con trolled switch G will be rendered conductive by the application of the positive voltage at the gate electrode thereof from the battery E. The turning off and spark output will be repeated upon opening the set of ignition points.

In the circuit of FIG. 3, another embodiment is shown which provides improved performance at high engine speeds. This circuit is substantially the same in structure as FIG. 1 except that a capacitor C1 is connected between the junction J1 and the gate electrode g of the gate controlled switch G. The operation of FIG. 3, however,- is somewhat different than that of FIG. 1, in that the gate controlled switch G is in its conductive, turned on state during a substantial portion of the switching cycle. Initially assuming the set of ignition points Si and the run-off switch S0 to be in their closed positions, the gate controlled switch G will be turned on, with current flow ing in the primary ignition coil W1 and the inductor L1. When the ignition points Si are opened, since the inductor L1 will not permit an instantaneous change of current, a negative voltage will be induced thereacross. This voltage will be applied through the capacitor C1 to the gate electrode g of the gate controlled switch G, which will then turn oft. A voltage will then be induced in the primary ignition coil W1 which will be transformed to the output secondary ignition coil W2 to serve as a spark output voltage similarly as discussed above.

The circuit including the capacitor C1, the inductor L1 and the gate controlled switch G are so designed to be slightly under damped, that is, during the transient period one positive overshoot of voltage will appear before there is a substantial attenuation of the oscillatory period of the circuit. This relatively large single positive voltage overshoot will apply a positive pulse to the gate electrode g which will turn on the gate controlled switch G again even though the ignition points Si are still in the opened position. Thus, current will again begin to flow and build up in the primary ignition coil W1 as soon as the gate controlled switch G is rendered conductive again, which permits a much longer time for the build up of energy in the primary coil. This permits a larger output spark voltage to be transformed to the secondary coil W2 upon the reopening of the anodecathode circuit of the gate controlled switch G. Better high speed operation of the engine results as may be seen from the following.

In the typical ignition system the ratio of on time (the time during which a spark output voltage is provided by the system) to off time (the time when energy is being stored in the system) is approximately one. It has been found that 200 microseconds is a sutficient period to supply adequately the spark output voltage from the secondary ignition coil. Even at 5,000 rpm. in an 8-cylinder engine, the time between sparks is approximately 3 milliseconds. The time constant (L/R) of a typical primary ignition coil is approximately 2 milliseconds. It can thus be seen, under the assumed conditions, that the primary ignition coil will not be carrying full current at the end of a half cycle of 1.5 milliseconds during which a conductive path is provided therethrough. When the circuit including the ignition coil is opened, since the primary ignition coil will not be carrying full current, a smaller spark output voltage will be supplied from the secondary ignition coil than would be supplied at lower engine speeds. Therefore, this results in an attenuation of the output spark pulse and poorer operation of the engine at high speeds.

The attenuation of the output spark voltage at high engine r.p.m.s is avoided in the circuit of FIG. 3 by the turning on of the gate controlled switch G after only a sufficient time has lapsed to permit the spark output pulse to be taken from the secondary ignition coil W2. The circuit components C1, L1 and the gate controlled switch are so selected, as discussed above, to establish proper damping. Moreover, the time constant of the circuit can be selected so that the positive overshoot of voltage will occur at approximately 200 microseconds after the turning off of the gate controlled switch G. This will permit sufiicient time to extract the output pulse'voftage. During the remainder of the cycle, even though the ignition points Si are opened, the gate controlled switch G will be conductive to permit current to build up on the winding W1. Thus, the total conductive time, in the assumed example of 5000 r.p.m. for an S-cyclinder engine, will be 3 milliseconds minus the 200 microseconds required for the output pulse to be generated. Using the typical standard ignition coil having a time constant of 2 miliiseconds, it can be seen that the current in the primary winding W1 will have reached substantially its steady state value before the gate control switch G is again turned off. Therefore, a substantially unattenuated output pulse voltage will be supplied even at high speeds since sufficient time is permitted for the build up of current in the primary ignition winding W1.

' Another ignition circuit which will provide improved high speed operationis shown in FIG. 4. This circuit is simiar to that of FIG. 1, however, a biasing circuit is provided to continuously maintain the gate controlled switch G in its conductive state during the entire switching cycle except for the time required to extract the pulse output voitage from thesecondary ignition coil W2. The biasing circuit includes a resistor R3 connected between ground and the gate electrode g of the gate control switch G. Connected to the resistor R3 and the gate electrode g are a plurality of series connected diodes D1, D2 and D3, with the cathode of the diode D1 connected to the junction I1 between the resistor R1 and the inductor L1. The anode of the diode D3 is connected to the resistor R3 and the gate electrode g. A conducting path is then provided from the positive electrode of the battery E, at ground potential, through the resistor R3, to the gate electrode 3, through the diodes D3, D2 and D1 to the junction J1.

With the switch S0 and the set of ignition points Si closed, the gate controlled switch G will be in its conductive state, current flowing in the primary ignition coil W1 and the inductor L1. Also, current will be flowing through the resistor R3 and the diodes D1, D2 and D3 so as to maintain a positive bias potential on the gate electrode g. Several diodes are required (three being shown) which have approximately a 1 volt voltage drop thereacross in their low impedance, current conducting direction so as to sufiiciently positively bias the gate electrode g with respect to the cathode electrode k. Upon opening the set of ignition points Si, a negative voltage is induced across the inductor L1 to counteract the sudden change of current in that circuit. Therefore, a negative pulse will be applied through the diodes D1, D2 and D3 to the gate electrode g of the gate controlled switch G which will thereby be rendered non-conductive. When the anode-cathode circuit of the gate controlled switch G is broken a voltage will be induced in the primary coil W 1 which will be transformed to the secondary coil W2 to supply an output spark voltage at the terminal To. After a sufiicient time has lapsed to generate the output spark voltage, which as discussed above may be of the order of 200 microseconds, the positive voltage applied through the biasing circuit including the resistor R3 and the diodes D1, D2 and D3 will turn on the gate controlled switch G immediately upon overcoming the induced voltage from the inductor L1. The time constant of the circuit including the inductor L1 can be selected so that a sufficient voltage will have dissipated after approximately 200 microseconds to permit the biasing potential applied to the gate electrode g through the biasing circuit to overcome this voltage and turn on the gate controlled switch G. Thus, the gate controlled switch G will be turned on again to permit current to build up in the primary ignition coil W1 even though the set of ignition points Si is still in its open position. Because of the increased time allowed for the build up of current in the primary ignition coil W1, even at high speeds a large magnitude output will be generated in the secondary coil as explained above in reference to FIG. 3. Upon the closing of the set of ignition points Si, the cycle will be repeated with a negative voltage being induced across the inductor L1 to apply a negative pulse to the gate electrode overcoming the positive bias potential thereon to render the gate controlled switch G again non-conductive.

If desired the ignition systems of FIGURES 3 and 4 could employ the configuration used in FIG. 2 to isolate the ignition points Si from ground if a negative ground ignition system is to be used.

The circuit components in the above described figures including the resistor R1, the capacitor C1 the inductor L1 are so selected that approximately one ampere will pass through the set of ignition points Si in each of the circuits. Moreover, a relatively low voltage of approximately 30 volts due to the circuit configuration will be applied at any period of time across the set of ignition points Si. Comparing these values to the 3 to 6 amperes at 300 to 40 0 volts usually applied in mechanical breaker point systems, it can be seen that the present system will have a substantially longer life-time. It has been shown by tests of circuits of the type presently disclosed that a lifetime of approximately five times that of the ordinary mechanical breaker type can be obtained.

It should also be noted that improved life of ignition points will be obtained because of the substantially similar turn on and turn off characteristic of the gate controlled switch G for each of the cycles. Thus, the ignition points -will open and close under substantially similar conditions which will tend to limit any Wide variations in arcing conditions and therefore attenuate degradation of the points even after substantial usage.

Although the present invention has been described to a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in the details of circuitry and the combination and arrangement of parts and elements may be resorted to without departing from the scope and the spirit of the present invention.

We claim as our invention:

1. An ignition circuit comprising, a gate controlled switch having anode, cathode and gate electrodes, an ignition transformer including a primary ignition coil operatively connected to the anode electrode of said gate controlled switch and a secondary ignition coil, an on-oif circuit including a set of ignition points, a capacitive device operatively connecting the gate electrode of said gate controlled switch to said on-ofi circuit, upon opening said ignition points a pulse being applied through said capacitive device to the gate electrode of said gate controlled switch to turn oif said gate control switch, a voltage being induced in said primary ignition coil and in response thereto an output spark voltage being induced in said secondary ignition coil, said gate controlled switch being turned on' after a predetermined time.

2. An ignition circuit operative with a source of direct current comprising, a gate controlled switch having anode, cathode and gate electrodes, an ignition transformer including a primary ignition coil operatively connected in series to the anode electrode of said gate control switch and a secondary ignition coil, an on-olf circuit including an inductive device and a set of ignition points operatively connected across said source, a capacitive device operatively connecting the gate electrode of said gate controlled switch to said on-otf circuit, upon opening said set of ignition points a voltage being induced in said inductive device to apply a negative pulse through said capacitive device to the gate electrode of said gate controlled switch and render said gate controlled switch non-conductive, a voltage being thereby induced in said primary ignition coil and in response thereto an output spark voltage being induced in said secondary ignition coil, said gate controlled switch being rendered conductive after a time determined by a circuit including said inductive and capacitive device being properly damped.

3. An ignition circuit comprising, a gate controlled switch including anode, cathode and gate electrodes, an ignition transformer including a primary ignition coil operatively connected to the anode electrode of said gate controlled switch and a secondary ignition coil, a turn oft circuit including a set of ignition points, a biasing circuit including an impedance device operatively connected to the gate electrode of said gate controlled switch and a plu- ,rality of unidirectional devices operatively connected between the gate electrode of said gate controlled switch and said turn otf circuit, said gate controlled switch being biased to its conductive state through said biasing circuit, upon opening said set of ignition points a pulse being applied to the gate electrode of said gate controlled switch to render said gate controlled switch non-conductive, an output spark voltage being induced in response thereto in said secondary coil, said gate controlled switch being rendered conductive again through said biasing circuit within a predetermined time after said output spark voltage is induced.

4. An ignition circuit operative with a source of direct current comprising, a gate controlled switch including anode, cathode and gate electrodes, an ignition transformer including a primary ignition coil operatively connected in series to the anode electrode of said gate controlled switch and a secondary ignition coil, said primary ignition coil and said gate controlled switch being operatively connected across said source, a turn 01f circuit including an inductive device and a set of ignition points operatively connected in series across said source, a biasing circuit including an impedance device operatively connected between said source and the gate electrode of said gate controlled switch and a plurality of diodes operatively connected between the gate electrode of said gate controlled switch and said turn off circuit, said gate controlled switch being biased to its turned on state through said biasing circuit, when said set of ignition points are closed a current path being provided through said inductive device, upon opening said set of ignition points a voltage being induced in said inductive device to apply a negative pulse voltage to the gate electrode of said gate controlled switch to turn off said gate controlled switch with an output spark voltage being induced in response thereto in said secondary coil, said gate controlled switch being turned on through said biasing circuit within a predetermined time after said output spark voltage is induced.

References Cited by the Examiner UNITED STATES PATENTS 2,955,248 10/1960 Short. 2,984,778 5/1961 Race. 3,045,148 7/1962 McNulty et a1. 123l48 X 3,213,320 10/1965 Worrell 123148 X OTHER REFERENCES SCR Designers Handbook by Westinghouse Electric Corporation, dated August 1963, pages 7-104 to 7-116 relied on.

MARK NEWMAN, Primary Examiner.

ARTHUR GAUSS, Examiner.

S. D. MILLER, L. M. GOODRIDGE,

Assistant Examiners. 

1. AN IGNITION CIRCUIT COMPRISING, A GATE CONTROLLED SWITCH HAVING ANODE, CATHODE AND GATE ELECTRODES, AN IGNITION TRANSFORMER INCLUDING A PRIMARY IGNITION COIL OPERATIVELY CONNECTED TO THE ANODE ELECTRODE OF SAID GATE CONTROLLED SWITCH AND A SECONDARY IGNITION COIL, AN ON-OFF CIRCUIT INCLUDING A SET OF IGNITION POINTS, A CAPACITIVE DEIVICE OPERATIVELY CONNECTING THE GATE ELECTRODE OF SAID GATE CONTROLLED SWITCH TO SAID ON-OFF CIRCUIT, UPON OPENING SAID IGNITION POINTS A PULSE BEING APPLIED THROUGH SAID CAPACITIVE DEVICE TO THE GATE ELECTRODE OF SAID GATE CONTROLLED SWITCH TO TURN OFF SAID GATE CONTROL SWITCH, A VOLTAGE BEING INDUCED IN SAID PRIMARY IGNITION COIL AND IN RESPONSE THERETO AN OUTPUT SPARK VOLTAGE BEING INDUCED IN SAID SECONDARY IGNITION COIL, SAID GATE CONTROLLED SWITCH BEING TURNED ON AFTER A PREDETERMINED TIME. 